Method for electrolytically polishing iron and iron alloys



United States Patent 3,389,066 METHUD F0 ELECTROLYTECALLY POLISHING IRON AND IRQN ALLOYS Yasuichi Shibasaki, Yokohama, Japan, assignor to Kyowa Hakko Kogyo Co., Ltd., Tokyo, Japan, a corporation of Japan No Drawing. Continuation of application Ser. No. 371,133, May 29, 1964. This application Sept. 14, 1967, Ser. No. 667,666

7 Claims. (Cl. 204-1405) ABSTRACT OF THE DISCLQSURE A method for electrolytically polishing iron or iron alloys to effect an uneven pear-like appearance thereon which comprises electrolyzing a solution consisting essentially of (a) water, (b) at least one compound selected from the group consisting of sulfuric acid, hydrochloric acid, nitric acid, sodium chloride, potassium chloride, calcium chloride, magnesium chloride, ferric chloride, sodium sulfate and ferric sulfate and an effective amount of (c) at least one additive selected from the group consisting of glue, agar, paper, starch, cellulose, glucose, fructose, sucrose, maltose, tannic acid, glycerine, saccharine, polyvinyl alcohol, polyethylene, higher fatty acids, acid hydrolysates of grass and active carbon at a temperature of from 0 to 100 C., a voltage of from 0.5 to 25 volts and a current density of from to 300 amperes per square decimeter, the metal to be polished constituting the anode, until the desired pear-like appearance is attained.

The present application is a continuation of application Ser. No. 371,183 filed in the United States Patent Office on May 29, 1964, and now abandoned.

The present invention relates to an electrolytic polishing solution and to a process of polishing therewith, more particularly to the electrolytic polishing solution for effecting a pear like appearance on the surface of iron and its alloys and the use thereof. The term pear-like appearance or pear appearance used in this specification means a surface similar to pear-skin or uneven, and it is to be construed in a somewhat broader sense including coarsely uneven and finely uneven surface with or without luster. The term iron alloy means all kinds of alloys composed of iron as a chief component, such as stainless steel.

One object of the present invention is to develop a pearlike appearance on the surface of iron and its alloys by electrolyzing.

Another object is to provide a chemical composition of electrolytic solution for pear-like appearance on the surface of iron and its alloys.

Further object is to provide a novel and economical process for obtaining iron and its alloys with a pear like surface by electrolytic polishing.

In the prior art for polishing iron or its alloy surface to a pear-like appearance, mechanical methods such as blasting of sand, alundum, carborundum or other particles onto the surface are Widely adopted. These prior arts, however, are disadvantageous because they not only are intricate but also often produce unfavourable stresses on the surface of the metals.

Patented June T13, 1963 "Ice The present inventor conducted research on the electrolytic polishing of iron and its alloys, and has found that when the electrolytic polishing of iron and its alloys is carried out by using an electrolytic solution containing at least one member selected from the group consisting of inorganic acids and the salts thereof, the surface of the metal is polished to give a pear-like appearance. Further, the present inventor has found that when substances having the property of adhering to the surface of iron and its alloys during electrolysis or of keeping small bubbles of generated gas or oxygen are present in the above-mentioned electrolytic solution, better effects are observed.

As to the inorganic acid used in the present invention, many kinds of acids may be used, and sulfuric acid and hydrochloric acid are most favourable. As to the salts of inorganic acids, also many kinds of salts may be used, and preferably sodium chloride, potassium chloride, calcium chloride, magnesium chloride, ferric chloride, sodium sulfate and ferric sulfate are used. The preferable concentration of acid or salt in the electrolyte depends greatly upon the kinds of acids and salts, for example, in the case of sulfuric acid, the concentration of 0.5-lll mol/kg. water is preferable and that of 1-4 moi/kg. water is the most optimum, while in the case of sodium chloride, the concentration of 0.01 mol/kg. water to saturation may be applicable and the optimum concentration is 1-5 mol/ kg. water.

In the present invention, electrolyte containing only at least one member selected from the group consisting of inorganic acids and salts thereof can be effectively used, however, as aforementioned, the better effects are obtained when the substances having the property of adhering on the surface of metal or the substances having the property of keeping the small bubbles of generated gas or oxygen are also present. This effect is not only achieved by adding substances, which originally have such a property, to the acidic electrolyte, but also by adding substances which are converted by inorganic acids or the salts thereof to the effective substances. Therefore, it should be understood that many kinds of substances may be used as additive substances. Moreover, more than two kinds of effective substances may be used together.

The electrolytic polishing of iron and its alloys by using sulfuric acid has already been known, but such polishing was conducted to obtain a mirror-like surface by using sulfuric acid of comparatively high concentration. Thus, the electrolytic polishing to obtain a pear-like surface is conducted for the first time by the present inventor.

When the preferable concentration of inorganic acids is adopted as the concentration of electrolyte,-the iron or its alloys as the anode are soluted (non-uniformly) and the pear-like appearance of the surface :is achieved. The effective substances having the afore-mentioned property adhere to the surface or keep small bubbles of generated gas or oxygen, thereby favoring non-uniform dissolution of the iron or its alloy surface. Thus, a fine pear-like appearance is obtained. This is the most: important principle of the present invention.

As to the additive substances which gives the better effect, many kinds of materials may be used both singly or in admixture and the following are examples; organic acids such as gluconic acid, tannic acid; oxalic acid; organic acid salts such as gluconic acid salts, oxalate; natural high molecular substances such as glue, agar and paper; carbohydrates such as starch, cellulose, glucose, fructose, sucrose and maltose; higher fatty acids; higher fatty acid derivatives; saccharine; polyhydric alcohols such as glycerine; synthetic high molecular weight substances such as polyethylene and polyvinyl alcohol; acidhydrolysates of grass.

The substances above-mentioned are generally efiective in themselves, but some substances such as paper change in the acid or salt solution and the changed substances are elfective, and moreover, sometimes the changed substances are more effective than the originals.

As to the electrolyzing conditions, the temperature of the electrolyte is not critical, however, l00 C. is suitable. In the case of iron, the temperature of between -10 C. is the optimum, while in the case of 188 stainless, the temperature of between 70-85 C. is optimum.

As to the voltage, 0.5-25 volt is suitable and the voltage depends largely upon the temperature of the electrolyte. When the voltage is higher than the indicated range, the polished surface tends to be mirror-like. In the case of higher temperature, the voltage should be low.

The anodic current density may vary depending upon the composition and the temperature of the electrolyte. The amperage of between 5 and 300 a./dm. may be suitable and is preferably -l00 a./dm.

In order to polish iron and its alloys to a fine and uniform pear-like appearance, the conditions above-mentioned should be kept within the optimum range considering the correlation between them.

The following examples show the nature of the present invention more specifically and they are for clarification but not for limitation of the present invention.

EXAMPLE 1 A solution consisting of 10 g. of sulfuric acid and 90 g. of water is used as the electrolyte. An iron plate having 2 mm. thickness and 0.09 dm. surface area is used as the anode and a lead electrode is used as the cathode. The electrolysis is carried out at 24 C., the bath voltage is 5 volts, and the current density is 5 a./dm. After 3 minutes, the iron plate is taken out and washed with water, the surface of the plate shows a fine pear appearance.

EXAMPLE 2 The same iron plate as in Example 1 is polished by using 6 N hydrochloric acid as the electrolyte. The temperature of the elecrtolyte is C., the bath voltage is 5 volts and the anodic current density is 20 a./dm. The polishing period is 10 minutes. The surface of the iron plate is polished to a fine pear-like appearance.

EXAMPLE 3 The same iron plate as in Example 1 is polished by using 3 N aqueous sodium chloride solution as the electrolyte. The temperature of the electrolyte is 1030 C., the bath voltage is 5 volts and the current density is a./dm. The polishing period is 5 minutes. The surface of the iron plate is polished to have fine pear-like appearance with little luster.

EXAMPLE 4 The same iron plate as in Example 1 is polished by using 1 N sodium sulfate as the electrolyte. The other conditions are the same as those in Example 1. The surface of the iron plate is polished to have the fine pear appearance.

EXAMPLE 5 An 18-8 stainless steel plate having 2 mm. of thickness and 0.09 dm. surface area is used as the anode. The polishing conditions are the same as those in Example 1. The surface shows a time pear-like appearance.

4 EXAMPLE 6 1 g. of filter paper is added t oa solution consisting of 165 g. of sulfuric acid and 52 g. of water at a temperature of 70 C. The filter paper is dissolved rapidly and the solution becomes dark. The solution is used as the electrolyte. An 18-8 stainless steel plate having 3 mm. thickness and.0.l3 dm. surface area is used as the anode, and a lead electrode is used as the cathode. The temperature of the electrolyte is 70 C., the bath voltage is 0.6 volt and the current density is 40 a./dm. After 5 minutes of electrolyzing, the stainless steel plate is taken out and washed with water. The surface shows a coarse pear appearance without luster.

EXAMPLE 7 Example 6 is repeated under the same conditions except that 5 g. of active carbon is used in place of the filter paper. The surface of the stainless steel shows a coarse pear appearance.

EXAMPLE 8 l8-8 stainless steel plate is electrolytically polished by using a solution consisting of 165 g. of sulfuric acid, 52 g. of water, 1 g. of filter paper and 10 g. of sodium gluconate. The electrolyzing conditions are as follows:

Temperature, 70 C.; bath voltage, 3 volts; current density, 40 a./dm. period of treatment, 8 min.

The surface of the stainless steel is polished to have a pear appearance.

EXAMPLE 9 A solution consisting of 5,500 g. of sulfuric acid, 1716 g. of water and 1800 ml. of 50% gluconic acid solution is used as the electrolyte. An iron plate is polished electrolytically to have a pear-like appearance.

EXAMPLE 10 A solution consisting of 235 g. of nitric acid, 1200 g. of sulfuric acid, 910 g. of phosphoric acid and 3,630 g. of water is used as electrolyte. An iron plate is polished electrolytically under the conditions of room temperature, 2 a./dm. of anodic current density and 5 volts of bath voltage. The surface is polished to have an appearance with no luster.

EXAMPLE 11 Run No 1 2 3 4 5 6 7 Composition of Electrolyte (mol/kg. water):

HzSOq 4.5 4 3. 7 2 8 3 5 1 Glueonic acid 5 1. 3 1 2. 5 1 2 0. 5 Sodium gluconate O. 7 Other materials 1 0.2 Temperature C.) 50 45 24 40 10 20 30 Bath voltage (v.) 5 6. 5 4. 5 5 8. 5 6. 5 5 Current density (a./d 200 143 186 151 100 Kind of stanless steel 18-8 18-8 18-8 18-8 2 13 18-8 Polished surface (pear appearance) 1 (FeSO*). 2 Chrome. 3 Fine with luster.

EXAMPLE 12 Run No 1 2 3 4 5 6 7 Composition of Electrolyte (Mol./kg. water): H2S04 5 Fear appearance with slight luster. 0 Fine pear appearance without luster.

EXAMPLE 13 Run N 1 2 3 4 5 Composition of elecirolyte. HCl, incl; H01, 10 mol; NaCl, 3 mol; H01, 5 mol; NaCl, 2 mol;

Gluconic acid, 60 gr; Gluconic acid, 30 g.; Sodium gluconate, E 304, 2 mol; Glue, g.; Water, 1 kg. Water, 1 kg. 25 g.; Water, 1 kg. Starch, 30 g., Water, 1 kg.

Water, 1 kg. (Heated for 20 min. at 100 C.) Temperature C.) 20 10 10-30 30 20. Current density (aJdm 10 25 10.. 20. Period (Min.) l 6 4 c 10.1. 10. Polished material Iron Iron and l3-Chrome Iron and 18-8 stainless Ire and stainless Iron stainless steel. steel. steel. Surface appearance after Coarse pear Fine pear Fine pear Fine pear Thin pear electrolyzing. appearance. appearance. appearance. appearance. appearance.

I elalm: 4. The method of claim 1, wherein the current density 1. A method for electrolytically polishing a metal selected from the group consisting of iron and iron alloys to effect a pear-like appearance thereon which comprises electrolyzing a solution consisting essentially of (a) water, (b) at least one compound selected from the group consisting of sulfuric acid, hydrochloric acid, nitric acid, sodium chloride, potassium chloride, calcium chloride, magnesium chloride, ferric chloride, sodium sulfate and ferric sulfate and an eifective amount of (c) at least one additive selected from the group consisting of glue, agar, paper, starch, cellulose, glucose, fructose, sucrose, maltose, tannic acid, glycerine, saccharine, polyvinyl alcohol, polyethylene, higher fatty acids, acid hydrolysates of grass and active carbon at a temperature of from 0 to 100 C., a voltage of from 0.5 to 25 volts and a current density of from 5 to 300 amperes per square decimeter, the metal to be polished constituting the anode, until the desired pearlike appearance is attained.

2. The method of claim 1, wherein said compound (b) is sulfuric acid in an amount of 0.5-1O mole/kg. of water.

3. The method of claim 1, wherein said solution also contains phosphoric acid.

References Cited UNITED STATES PATENTS 1,995,766 3/1935 Chester 204- 2,270,712 1/1942. WOOd 252-79.4 2,542,779 2/1951 Neill 204--140.5 2,687,346 8/1954 McDonald 252-794 2,690,001 11/1954 Hayes et al. 252----79.4 2,773,821 12/1956 Smith 204140.5 3,213,008 10/1965 Valentin 204-1405 ROBERT K. MIHALEK, Primary Examiner. 

